If an invalid initarg is used an appropriate error message is generated:

? (make-instance 'ship :x 5 :y 7 :z 9)
> Error: :Z is an invalid initarg to INITIALIZE-INSTANCE for
>#<STANDARD-CLASS SHIP>.
>        Valid initargs: #(:Y :X).
> While executing: CCL::CHECK-INITARGS
> Type Command-. to abort.
See the RestartsŠ menu item for further choices.
1 >

The example demonstrates that initargs (keywords) need not be associated with
slots but can be declared with methods (for initialize-instance).

rm

[ Sorry if you receive multiple copies of this message ]